n = int(input())
c = input()

print(c[:c.count('R')].count('W')) n = int(input()) n int(input()) int input() input c = input() c input() input print(c[:c.count('R')].count('W')) print c[:c.count('R')].count('W') [:c.count('R')].count [:c.count('R')] c :c.count('R') c.count('R') c.count c count 'R' count 'W' n = int(input()) int(input()) n c = input() input() c
n = int(input())
c = input()

print(c[:c.count('R')].count('W'))
